1. Field of the Invention
The present invention relates to a thermal transfer sheet used for a thermal transfer printer performing transfer by heating using a thermal head or the like, and, particularly, to a scratch layer thermal transfer sheet which can hide information recorded on, particularly paper or a card such that the information is made indistinguishable easily as it is and besides, the hidden part can be easily scratched off by a nail or a coin, and further relates to a method using the scratch layer thermal transfer sheet and a transfer-receiving material to produce a scratch printing product.
2. Description of the Related Art
Print products with a hidden image disposed under a hiding ink layer, which image is allowed to emerge by scratching off the hiding ink layer using a nail or a coin to thereby scrape it, are currently used generally for lottery tickets, prepaid cards and the like. These print products respectively have a structure in which an image including characters and designs is printed on the surface of an opaque substrate such as a plastic film, paper or synthetic paper by using printing ink, solid printing is made on the entire surface by using opaque ink in such a manner as to cover the whole printed image and the surface of the image is hidden by a peelable ink layer.
Also, such a method is currently adopted in which using a thermal transfer sheet formed with a thermal transfer layer on a substrate, the thermal transfer sheet is heated imagewise from the backface thereof by using a thermal head to form an image constituted of variable information and, further, using a thermal transfer sheet provided with a thermal transfer layer capable of being a hiding layer, the thermal transfer layer is thermally transferred to the surface of the image, without forming a hiding ink layer by a printing method using a plate, to thereby hide the image.
However, even if a thermal transfer sheet provided with a thermal transfer layer having hiding ability is used with the intention to hide information recorded on a card or the like such that the information is made indistinguishable easily as it is by thermal transfer, there is the case where the following problem arises when the recorded information is accompanied by an irregularity (for example, in the case of recording information by thermal transfer, ink is stuck only to the transfer portion and only this portion therefore rises). Specifically, even if the hiding ink layer has a hiding capability enough to prevent the underlying display from being seen through, the surface resultantly follows the irregular pattern and a difference in surface glossiness with the result that the recorded information can be read.
Also, if a substrate as a medium on which information is recorded is a medium having a low surface smoothness, such as paper, there is the problem that the hiding layer cannot be easily scratched off on account of an anchor effect.
In addition, conventionally, a thermal transfer sheet provided with a hiding thermal transfer layer which can be scratched off and a thermal transfer sheet for information recording are separately prepared. First, thermal transfer recording is made on a transfer-receiving material by using the thermal transfer sheet for information recording. Next, the thermal transfer sheet is exchanged with the thermal transfer sheet provided with the hiding thermal transfer layer to hide the recorded part This method poses the problem that two types of thermal transfer sheet are used for one print product and therefore troublesome works for exchanging these thermal transfer sheets and material cost are needed.